1. Field of the Invention
The present invention relates to a low-frequency electrotherapeutic device.
2. Description of the Related Art
Conventional low-frequency electrotherapeutic devices are generally of a structure in which there is provided a pair comprising a different electrode and an indifferent electrode, with the paired electrodes being used alone as electrodes for medical treatment. Exceptionally, in Japanese Patent Application Laid-Open No. 63-192459, there is proposed a low-frequency electrotherapeutic device wherein five pairs are provided, each pair comprising a dot-like positive electrode 101 and an annular negative electrode 102, as shown in FIG. 7. In this low-frequency electrotherapeutic device, although five pairs of different electrodes and indifferent electrodes are arranged in a rectangular shape, the structure thereof can be regarded as essentially using only a single pair comprising a different electrode and an indifferent electrode. In Japanese Patent Application Laid-Open No. 63-257577, there is proposed a low-frequency electrotherapeutic device having a different electrode 103 and an indifferent electrode 104 which are concentric with each other, as shown in FIG. 8. The structure of this low-frequency electrotherapeutic device can also be regarded as including only a pair comprising a different electrode and an indifferent electrode. Further, in Japanese Patent Application Laid-Open No. 62-137067 is proposed a low-frequency electrotherapeutic device wherein three electrodes are arranged in parallel, with the central electrode being used as an indifferent electrode while the electrodes located at either side of the central electrode are used as different electrodes which are simultaneously supplied with an electric current. However, even in the low-frequency electrotherapeutic device described in Japanese Patent Application Laid-Open No. 62-137067, the two different electrodes are electrified simultaneously; hence the structure of the device can also be regarded as essentially using a single pair comprising a different electrode and an indifferent electrode.
Thus, each of the conventional low-frequency electrotherapeutic devices referred to above consists essentially of a single pair comprising a different electrode and an indifferent electrode, wherein the positional relationship between the different electrode and the indifferent electrode is fixed. An electrical circuit, through which a stimulating current flows from the positive electrode to the negative electrode, is always formed at a limited position of the skin of a living body; that is, stimulation is repeated at the same position adjoining the skin of the living body. Continuing the electric stimulation at such a limited position on the living body skin is discomforting to the living body and makes the stimulation less effective due to habituation.
The above-described problems in relation to the stimulating current being applied at the same position of the body occur even in the structure wherein a different electrode and an indifferent electrode are connected through lead wires to a controller so as to allow the distance between both electrodes on a living body to be freely changed, or even in the structure having five pairs, each pair comprising a different electrode and an indifferent electrode, such as that shown in FIG. 7, because once the different electrode(s) and the indifferent electrode(s) are attached to a living body, their positional relation becomes fixed. Therefore, the foregoing problems have been solved by neither the low-frequency electrotherapeutic devices presently available in the market nor those proposed in the past.
In efforts to solve the above-mentioned problem, there have heretofore been conducted studies regarding the method of varying the voltage waveform outputted from a different electrode so as to thereby automatically change the type of stimulation in the range of at least three patterns and at most seven or eight patterns, as shown in FIGS. 9 and 10. Sine wave F, square wave G and exponential wave H are composite variations of group waveform I in all. These are considered to be a factor of time (both fast and slow K) and considered to be variations in periods T1-T4 in FIG. 9. The factor of strength M is considered to be variations in voltages V1-V4 in FIG. 9 producing different strength outputs.
However, even if the width and magnitude of each pulse in the pattern are changed shown in FIG. 9, or the stimulation pattern is changed as in FIG. 10, the human becomes less sensitive to such stimulating current. That is, any person, in his or her neural response, exhibits a tolerance against stimulation repeated at the same position on his or her body. As a result, no matter how the type of stimulation may be changed, the person loses sensitivity in discriminating between stimulation with respect to the type and strength. This phenomenon is well known within the field of physiology. Consequently, even with stimulation pattern changed as in FIG. 10, for example, even if a weak stimulation is given to a human just after a strong stimulation (such as voltage V2 after V1 or voltage V4 after V3 in FIG. 9), the human can no longer sense it as stimulation. The longer continued the stimulation, the more marked this tendency.
Thus, according to the electrode structure of the conventional low-frequency electrotherapeutic devices wherein the positional relationship between a different electrode and an indifferent electrode is fixed, a patient being treated by the device exhibits a tolerance in his or her neural response, with the result that the effects of treatment for diseases of the nervous system such as neuralgia and palsy of the peripheral nerve, which treatment effects are clearly mentioned to be provided by the electrotherapeutic devices, become deteriorated with the lapse of working time of the devices.
In addition to the above problem relating to the tolerance in neural response, there also has been the problem that an electric charge is accumulated in the human living body tissue due to the electric current outputted from the low-frequency electrotherapeutic devices. More particularly, as long as the positional relation between the different electrode and the indifferent electrode within each such low-frequency electrotherapeutic device remains fixed, the path of electric current also becomes fixed and the aforesaid accumulation of electric charge in the living body also occurs at the same position. As a result, the waveform of the output voltage from the different electrode is greatly distorted; therefore, a stimulating electric current has difficulty in flowing through the living body and the patient undergoing medical treatment feels stimulation only to an extremely slight degree.
Due to the aforesaid accumulation of electric charge in the living body caused by continued stimulation at the same position of the living body, effects of massage such as the recovery from fatigue and the promotion of blood circulation are also deteriorated.
Even apart from the problems caused by the tolerance in neural response and the problems caused by accumulation of electric charge in the living body, the repeated electric stimulation at the same position of the living body causes discomfort.